Many applications for plastic materials require the use of colorants. Such colorants can be dyes, organic pigments, and inorganic pigments. Colorants can be in the form of dry powders or they can be concentrates with a high loading of color in the polymer used.
Of the methods used to color a plastic material, one of the simplest is barrel blending, wherein a measured portion of colorant is admixed by tumbling, with a measured portion of natural (uncolored) plastic material. Barrel blending, however, is not well adapted to large volume applications. Some commercial applications generally utilize large tank blenders, wherein measured portions of materials to be blended are placed in the tank blender and blended material is withdrawn from the tank when blending is completed. Where blending is performed in batch functions, the blended materials must be stored until they are utilized by the processing machinery (i.e. molding, spinning, etc.). This, however, results in some problems due to the blended material separating prior to its use. One method of resolving this problem is by direct proportionate feed from a storage facility to the processing machinery.
One example of direct proportionate feeding is the use of a weigh belt feeder system. The simplest such system involves a natural and a color concentrate pellet storage hopper pellet storage hopper with each hopper having its own weigh belt conveyor. The two conveyors discharge into a common receptacle, as for example, the feed hopper of an extruder. While such systems offer some advantages over batch handling systems, they are, nevertheless, not without drawbacks. For example, they can be expensive to maintain. Moreover, since this method of proportionate feeding is dependent upon precise measuring and feeding devices, calibration problems often arise.
Historically, as customer demands for better control of color level have increased, more sophisticated and expensive control equipment has been employed, rather than seeking out less expensive, less complicated equipment. It is therefore an object of this invention to provide an improved apparatus for the proportionate feeding of particulate solids.
Other objects, aspects and advantages of the present invention will become apparent to those skilled in the art upon reading the following detailed description when considered in connection with the accompanying drawings and the appended claims.